Salt flat
]] lakebed]] Dry lakes are an ephemeral lakebed, generally extending to the shore, or a remnant of an endorheic lake. Such flats consist of fine-grained sediments infused with alkali salts. Dry lakes may be known as alkali flats, sabkhas, playas or mud flats. If the surface is primarily salt then they are called salt pans, pans, hardpan, salt lakes or salt flats. Terminology The Spanish word playa ( ) literally means "beach". Alkali flats are known by this name in some parts of Mexico and the western United States. On the Llano Estacado and other parts of the Southern High Plains, playa refers to a dry lake, a smaller seasonal depression. In South America, the usual term for a dry lake is salar, Spanish for "salt pan". Pan is the term used in most of South Africa. These may include the small round highveld pans, typical of the Chrissiesmeer area, to the extensive pans of the Northern Cape province, which are sometimes employed for land speed record attempts. It is also used in Australia. Distinguished are salt pans and clay pans. Hardpan is a dry terminus of an internally drained basin in a dry climate, typically used in the Great Basin of the western US. In Arabic, an alkali flat is called a sabkha (also spelled sabkhah, subkha or sebkha) or shott (chott). In Central Asia, a similar "cracked mud" salt flat is known as a takyr. In Iran salt flats are called kavir. Formation after the exceptionally wet winter and spring of 2005, Death Valley National Park.]] The surface of a dry lake is typically dry, hard and rough during the dry season, but wet and very soft in the rainy season. Dry lakes may be small, round depressions in the surface of the landscape. A playa lake is formed when rain fills this hole with water, creating a small lake. Dry lakes can also form when the water table intersects the surface and water seeps into them. Dry lakes are typically formed in semi-arid to arid regions of the world. The largest concentration of dry lakes in the world (nearly 22,000) is in the southern High Plains of Texas and eastern New Mexico. Most dry lakes are small, however Salar de Uyuni in Bolivia, near Potosí, the largest salt flat in the world is of 4,085 square miles (10,582 square km). Many dry lakes contain shallow water during the rainy season, especially during wet years. If the layer of water is thin and is moved around the dry lake by wind, an exceedingly hard and smooth surface may develop. Thicker layers of water may result in a "cracked-mud" surface and "teepee" structure desiccation features. Very little water can result in dune formation. Ecology While the dry lake itself will be devoid of vegetation, they are commonly ringed by shadscale, saltbrush and other salt-tolerant plants that provide critical winter fodder for livestock and other herbivores. Threats to dry lakes include pollution from concentrated animal feeding operations such as cattle feedlots and dairies, erosion, fertilizer, pesticide and sediment runoff from farms, and overgrazing. Human use chemical plant processes brines from Searles Dry Lake to make such products as trona]] The extremely flat, smooth and hard surfaces of dry lakes make them ideal for motor vehicles and bicycles. Furthermore, large-sized dry lakes are excellent spots for pursuing land speed records, as the smoothness of the surface allows low-clearance vehicles to travel very fast without any risk of disruption by surface irregularities, and the path traveled has no obstacles to avoid. The dry lakes at Bonneville Salt Flats in Utah and Black Rock Desert in Nevada have both been used for setting land speed records. Dry lake beds that do not fill with water at any time are sometimes used as locations for air bases, for similar reasons. Examples include Area 51 in Nevada, and Edwards Air Force Base (originally known as Muroc Dry Lake) in California. Brines from the subsurface of dry lakes are often exploited for valuable minerals in solution. See, for example Searles Dry Lake and Lithium resources. United States regulation Under United States law, a "playa lake" may be considered isolated wetlands, and may be eligible to enroll in the new wetlands component of the Conservation Reserve Program, enacted in the 2002 farm bill (P.L. 107-171, Sec. 2101). Gallery Image:Lake Hart.jpg| The dry lake and shore of Lake Hart, an endorheic desert lake in South Australia. Image:Piles of Salt Salar de Uyuni Bolivia Luca Galuzzi 2006 a.jpg| Salt harvesting in Salar de Uyuni, Bolivia, the world's largest salt flat. Image:Jfader playa.jpg| A closeup photograph of salt growths on the crust of a dry lake. Image:EtoshaPan 2005-06 comparison.jpg| Etosha Pan in northern Namibia See also * Soil salinity * Cienega References Bibliography * *John H. Wellington, "Southern Africa: a geographical study", Chapter 16 LAKES AND PANS External links * The Bibliography of Aeolian Research Category:Salt flats Category:Spanish loanwords Category:Aeolian landforms Category:Fluvial landforms ar:سبخة cs:Playa de:Salztonebene id:Playa no:Saltslette pl:Playa ro:Playa fi:Aavikkojärvi